ARG0002qrr amazing double lobe (4C +14.54)
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by
JeanTate
very bright, almost compact lobes, twin jets with distinct local maxima. Lots of NED references, but none seem to associate it with SDSS J144426.48+140014.2, which coincides with the bright, apparent IR core/host. It's a z=0.522 giant elliptical, with an AGN with extremely strong (and narrow) emission lines (esp [OIII])
What does the structure in the jets/lobes tell us?
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WizardHowl
questions I would add to this are: why are the outermost plumes brightest? these are separate plumes from FIRST as if restarted, not hot spots in diffuse lobes? I would have thought that the innermost pair would be the younger pair, which would imply that there was 1) not much time between the two eruptions 2) the jets were less tightly collimated for the second eruption?
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akapinska
scientist
The questions may seem innocent, but there's a lot of physics behind this! 😉
We agree that the central galaxy (IR host) ejects two relativistic outflows, i.e. jets. This radio galaxy beside looks like one of the most powerful type (so called Fanaroff-Riley type II = FRII), and so its jets are powerful enough to go well beyond the host galaxy. But the jets will not expand to infinite distances, and eventually will terminate - the external medium in which the jets expand may eventually become too dense to penetrate for them. And this is the moment when the so-called hot spots are being formed.
Once the hot spot is formed the jet will not extend beyond it (this is the termination point) but meanwhile a number of shocks are formed and what happens in the end is that the material transported by the jets to the hotspots now will be moved back towards the IR host - this is how the radio lobes are formed, and that will be the diffuse emission you can see here.
Now, the shape of the jets/lobes can be altered from perfectly symmetrical (which let's call the default) depending on how dense and clumpy the external medium around the host galaxy is. So, these radio structures really probe the environment!
So this is what the structure really tells us (we can translate it to a variety of physical measurements of course) and that is the reason why the outermost part of the signal is the brightest. But, beware, this is only valid for FRII types (doublelobe, hourglass in hashtags), but not FRI types (plumes, in hashtags within RGZ).
As for the re-starting question of @WizardHowl, the general idea of how the restarted source would look like that you have is correct, but this source is not restarted. First of all, the inner most pair should be the brightest - it is clearly not the case here, and you would clearly see two separate pairs of lobes, which is also not the case here. As to how long it takes for the radio galaxy between the old and new activity is still very much under debate between scientists, but estimates based on quite few examples of restarted radio galaxies that we have tell us it may be around 0.4 - 140 Mega years. IF of course the models we use are good enough!
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